In a wireless mobile communication system, as a UE (User Equipment) can move during communication in progress, a traffic channel environment may vary in time. Because a different communication scheme may be appropriate for each traffic channel environment, a BS (Base Station) needs to determine a specific communication scheme and signal the determined communication scheme to the UE on a control channel according to passage of time. The UE may transmit control information needed for the BS to determine the specific communication scheme to the BS on an uplink control channel.
When a control channel and a traffic channel are simultaneously transmitted, the BS can transmit them using all resources without any restriction because it can supply sufficient transmission power. On the other hand, when the UE is to transmit a control channel and a traffic channel at the same time, the waveform of a transmission signal may experience undesired distortion because the UE has limited transmission power and may not have good power amplifier characteristics. Especially in a 3GPP LTE (3rd Generation Project Partnership Long Term Evolution) system, a UE transmits a time-domain modulated signal in DFT-S-OFDM (Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing) to maintain the single carrier property, for optimizing the power of the UE. Despite the advantage of a remarkable decrease in CM (Cubic Metric) or PAPR (Peak-to-Average Power Ratio), the DFT-S-OFDM scheme has the shortcoming that a transmission signal is transmitted only in a contiguous frequency band. This imposes a constraint on simultaneous transmission of a control channel and a traffic channel. Therefore, when a control channel and a traffic channel are simultaneously allocated to a UE, the control channel and the traffic channel are designed such that a signal to be transmitted on the control channel is relocated to the traffic channel.
With the above channel configuration, the single carrier property can be maintained but, in fact, signal coverage is decreased rather than it is extended or maintained. For example, if a transmission signal is to be transmitted on an uplink traffic channel in the presence of a control channel designed for transmission of an ACK/NACK (acknowledgment/negative-acknowledgment), an ACK/NACK bit is mapped to an OFDM symbol around an uplink demodulation reference signal in a conventional technology. As a result, power available to the UE for transmission of the ACK/NACK signal is reduced to or below a half of a maximum energy that can be accumulated in a single subframe. Accordingly, the technique taken for CM reduction only reduces the link coverage of the control channel. Moreover, a problem caused by mixture between information of the control channel and information of the traffic channel affects the robustness of a protocol.
The conventional method presents no security solution when a UE fails to receive a command, for example, a scheduling grant from a BS and causes obscurity according to a control channel type. For example, when the UE transmits a Scheduling Request (SR) or it transmits an RI (Rank Indicator) suitable for a current channel along with a CQI (Channel Quality Information), the BS is not aware of the transmission and thus performs blind detection. However, a protocol-related problem may still occur. The present invention relates to a technique for generating a signal, while correcting such an error.